1. Field of the Invention
The present invention relates to an optical coherence tomographic apparatus, for example, an optical coherence tomographic apparatus which is used for ophthalmic care and the like.
2. Description of the Related Art
Currently, various ophthalmic apparatuses using optical apparatuses are known. For example, various apparatuses such as an anterior ocular segment imaging apparatus, fundus camera, and SLO (Scanning Laser Ophtalmoscope) are used as optical apparatuses for the observation of an eye to be examined. Among these apparatuses, an optical coherence tomographic apparatus based on OCT (Optical Coherence Tomography) using multiwavelength light wave coherence can obtain a tomographic image of a sample at high resolution. The apparatus is becoming indispensable to outpatient clinics specialized in retinas as an ophthalmic apparatus. This apparatus will be referred to as an OCT apparatus hereinafter.
An OCT apparatus irradiates a sample with measurement light which is low-coherent light, and can perform high-sensitivity measurement of backscattered light from the sample by using an interference system or interference optical system. Low-coherent light has the property of being able to obtain a high-resolution tomographic image by increasing the wavelength width. In addition, the OCT apparatus can obtain a high-resolution tomographic image by scanning measurement light on a sample. Therefore, the OCT apparatus can obtain a tomographic image of the retina at the fundus of an eye to be examined, and hence has been widely used for ophthalmic care and the like for the retina.
On the other hand, the OCT apparatus as an ophthalmic apparatus is generally equipped with optical systems for fundus observation, anterior eye observation, and the like to implement alignment adjustment between the apparatus and an object to be examined. In order to use the OCT apparatus together with these optical systems, the apparatus is configured to use light of different wavelengths for the respective optical systems and perform wavelength separation by using a wavelength separation unit such as a dichroic mirror. However, since low-coherence light having a wavelength width is used for the OCT apparatus, it is difficult to separate the wavelength of light used by an optical system for fundus observation, anterior eye observation, or the like from the wavelength of light used by the OCT apparatus.
According to U.S. Pat. No. 5,537,162, a beam scanner position is set on the back focal plane of a lens to make the incident angles of beams on dichroic mirrors constant even when performing beam scanning. This can unify the characteristics of the dichroic mirrors and increase the accuracy of wavelength separation.
According to U.S. Pat. No. 5,537,162, however, when performing focus adjustment for the fundus of an eye to be examined, the beam scanner and the lens are driven together. The lens having the back focal plane disposed on the beam scanner tends to increase in size to capture scan light from the beam scanner. It is therefore necessary to move the beam scanner together with the large lens. This increases the complexity of the driving mechanism. In addition, since they are moved together, it is necessary to simultaneously move a measurement light source optically conjugate to the fundus position. If this measurement light source is placed on an optical fiber end, it is necessary to move the optical fiber. This may change the polarization state.